Chewskt dit apostoloff



8 Sheets-Sheet 1.

(No Model.)

S. BERDITSCHEWSKYDIT APOSTOLOFP:

M. FRBUDBNBBRG.

(No Model.) 8 Sheets-Sheet 2. S. BERDITSCHEWSKY'DIT APOSTOLOFF 8v M. PREUDBNBBRG. SELEAGTING GOMMUTATQE EOE TELEPHONES.

N0.546,725. y Patented sept.24,1895.

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Patented Sept. 24, 1895.

No. 546,725. FEE.

Z @TM nREw BJinAMAM. PMOTO-UI'NUMASMINGTDMuC (No Model.) @Sheets-Sheet 5. S. BERDITSCHEWSKY DIT APOSTOLOFF 8v M. FREUDBNBERG. SELF ACTING GOMMUTATOR FOR TELBPHONES.- No. 546,725. Patented Sept. 24', 1895,.

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(No Moagl.) 8 sheets-sheen '6. S. BERDITSCH'EWSKY DIT APOSTGLOFF 8v M. FREUDENBERG. SELF ACTING GOMMUTATOR FOB. TELEPHONES.

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(No Model.) ,i 4 s sheets- Sheet 7. S. BERDITSCHBWSKY DIT APOSTOLOFF 8v Mt FREUDENBBRG. vSELF ACTING GOMMUTATOB, PoR TELEPHONES.

(No Model.) s sheets-sheet 18.'

S. BERDITSCHEWSKY DIT APOSTOLOFF 8a MF'RBUDENBBRG. SELIIZIAOTING COMMUTATOR FOR TELEPHONES.

o nl o e. n ci o o con a ne 0 e noo 0o o .o epe ce o o a o o no oo n o o o.. el 00.0 con o o. l o. ooge o o n .o a on. o o o o au ooe AN DREW BLRANANL PMOTOUTHUWASNINGYUN. nic

irnoTA'ES ATENTv .,Fnrcn.

SALOMON nnnorrsonnws-KYv DIT APosToLOEE AND Moise FREUDENBERG,

- or PARIS, FRANCE. 1

SELF-ACTING OOMMUTAITOR FOR TELEPHONES.

SPECIFIGATIQN forming part of Letters Patent No. 546,725, dated September 24, 1895.

Application filed March 27, lili-)5. Serial No. 543,412- (No model.)

siding at Paris, France, have invented certain.

new and useful Improvements in Self-Acting Commutators for Telephones, which improvements are fully described in the following specification. v

The central office, which puts the subscribers of a telephonie exchange in communication with one another in conformity withtheir directions, requires (as Ordinarily conducted) Va considerable number of employs, whose services are a cause of very large expense, generally, in the working of a telephone-exchange. It is with a view of remedying this inconvenience, and also of increasing the rapidity of telephonie communications, that we have invented the present system of automatic switching apparatus, which permits any subscriber to put himself in communicationlwith any other without requiring thein-l tervention of employs at a central office, whatever may be the number of the subscribers of the exchange.

An automatic switching apparatus for telephones for serving an indefinite number of subscribers should satisfy the following conditions: first, it should require only one wire to a subscriber; second, it should occupy little space, not more in any case than the apparatus which actually exist in central offices; third, the management should be easy, as also repair, in caseof derangement; fourth, it should operate with rapidity and with absolute precision, while requiring only a minimum expenditure of electric energy. These are the essential conditions which we have sought to realize 'in the automatic switching apparatus for telephones which constitutes the present invention.

Before entering into the full study of our apparatus we will first explain the principal means on which it is based. Suppose that in a given room of a telephone-exchange corresponding to the existing central office there is a surface of ebonite or other appropriate material on which, at equal distances apart, are disposed contacts that are connected exclusively each with the wire of a single subscribers line, and assumefor a moment that on this ebonite surface a metallic point connected with a subscribers Wire to whose use the surface and contacts mentioned are appropriated ismovable. By providing each subscriber a contact-plate composed of a similar surface and contact at the central Office, if any one of the subscribers can at will at his own house shift the corresponding point on the contactplate he can evidently connect himself with any other subscriber of the exchange Without the intervention Ofan employ, the role of the latter being taken by the devices in question. The point need not be shifted in a straight line, for with a considerable number of subscribers the path which the point would have to traverse would be overlong. To obviate this inconvenience, we have conceived of utilizing a system of co-Ordinates, rectilinear or not-that is to say, of giving to the vsubscriber the ability to shift the point not only in one direction but in two nonparallel directions-say, two lines oblique to each othe r,or a circle and a radius, or, further, two series of concentric circles. The advantage of shifting the point, not merelyin one direction, butin two non-parallel directions, will be at once perceived, if we take perpendiculars as an example. In the first case (one direction only) if the point in being shifted passes over X contacts, it will pass over X2 in the second case (two non-parallel directions) within substantially the same distance from the startingpoint. The displacement of the pointin each direction may therefore be small, although there are a large number of contacts on the plate. It only remains, therefore, to find a means whereby the subscriber is able, at his house and with few manipulations, to shift the point above the corresponding plate at the central office to receive signals as required, to establish telephonie communication, and then to return all the parts of the mechanism to their original positions.

Having thus briefly explained the principles of oursystem of automatic switching apparatus for telephones, we will study in detail those arrangements which We have devised for practically carrying it into effect, reference being made to the accompanying drawings, in which an automatic switching IOO apparatus in accordance with our invention is illustrated by way of example.

Figure 1 is a plan view of a subscribers switchboard at the central office. Fig. 1bis is a detail view showing some of the principal parts on a larger scale. Fig. 2. is a front elevation of the switchboard. Fig. 3 is a seetion on line 1 .2 of Fig. 1. Fig. 4. is a detail view, partially in section, ofthe mechanism for 1o shifting one of the electromagnets above the contact-plate. Fig. 5 is a section on line 3 et of Fig. 1, showing the carriage of the other electromagnet. Figs. 6 and 6bis are front and side elevations, respectively, of our special electromagnetic relay, whose function will be explained hereinafter. Figs. 7 and 7bis are plan and section, respectively, of a special switch placed at the side of each subscribers switchboard at the central office. Fig. 8 is 2o a frontview of the mechanism at the subscribers station, the telephonie apparatus of Aders system, in common use in France, being represented. Figs. 9 and 10 are views, in planes at right angles to that of Fig. 8, of devices at opposite sides of the said mechanism. Figs. 1l and 11bis are plan views showing the commutator belonging to said mechanism in the two positions which it can occupy. Fig. 2 is a perspective view of a sub-station appa- 3o ratus of Aders system provided with mechanism in accordance with the present invention. Figs. 13 and 1+i are views in plan and section, respectively, of a switchboard at the central office, in which the point, instead of moving in two perpendicular directions, can be shifted about two points taken as centers; and Figs. 15, 152, and 15d represent, respectively, in diagram,the apparatus at three subscribers stations X, Y, and Z, with the appara- 4o tus corresponding to each at the central office.

In our new or improved automatic switching apparatus there are two parts: first, the apparatus with movable point, which is installed at the central office, and, second, the mechanism or manipulator combined with the telephonie apparatus and placed at the domicile of each subscriber. We will consider successively each of these, and then describe in detail their operation, availing ourselves (for 5o this latter study) of the diagrams Figs. l5,

15, and 151.

The movablepoint apparatus is composed of two ebonite plates A B and C D, Fig. 3, disposed horizontally one over the other. On these two plates are fixed contacts, (contacts a on the upper plate and contacts b on the lower plates.)

In the central oflce there are for each subscriber two metallic bands, one of which 6o passes under all the lower plates at the central office and the other passes overall the upper plates, there being at the central ofiice as many switchboards composed of an upper and a lower plate as there are subscribers lines. In each switchboard the metallic bands corresponding to each subscribers line-wire are connected with two contacts, respectively, one

contact being in the upper and the other in the lower plate, and so placed as to bein the same vertical line. Between each pair of parallel plates A B and C D moves apoint S', which is a permanent magnet loosely placed in the interior of a solenoid S2. According to the direction of the current through the solenoid, the point can move up or down within said solenoid. Normally-that is to say, when the solenoid is without currentthe point S', acted upon by a spring, tends constantly to make contact with the lower plate. The point S forms part of a double carriage system, of which one carriage F', Fig. l, is movable in the direction M N, while the other carriage F2 is movable in the direction K L or in directions parallel thereto. The carriage F2 is forced to go with the carriage F', but it is movable in the direction K L (or a parallel direction) independently of the cat'- riage F'. On the carriage F' is mounted the electromagnet E', (see Fig. 4,) provided with an armature 1, held by a spring 2 constantly away from the magnet-poles and against a stop. To the lower end of the armature a pawl 3 is jointed, said pawl having a hook t for engaging the underlying ratchet 7. A second hooked pawl 5 is jointed to the carriage at 6 and engages the same, ratchet,

which extends widt-hwise of the switchboard.

When the electromagnet E' is traversed by a current, it attracts the armature 1 and advances the hook 4 of pawl 3 over the next tooth of the ratchet, which it then engages, so that on the interruption of the current the spring 2 advances the carriage the length of one tooth to the left and at the same time shifts the pawl 5 to a new tooth. At each new passage and cessation of the current the same phenomena are repeated and the ear- .riage F is advanced step by step, the length of one tooth at each step. By a series of currents, therefore, traversing the electromagnct E',the carriage F' is made to move toward the left an equal number of tooth-lengths.

To the carriage F' are fastened the two horizontal bars 9 and l0, which form the ways for said carriage F2 and which support the ratchet therefor. lVhen, therefore, the carriage F is moved in the direction MN, the carriage F2 on the bars 9 and 10 goes with it, andthe whole system thus moves to the left across the contact-plate. When the carriage Fhas been brought to the position which .it should have selectively to the contact-plate, the carriage F2 can be moved relatively to the carriage F' by sending a series of currents through the electromagn et E2, which advances the carriage F2 step by step along the bars 9 and 10 in a direction parallel to KL in the same manner as the carriage F' is moved in the direction MN. Of course if the carriage F' occupies the position shown in Fig. 1 the carriage F2 would move in the same direction of the line KL and not in aline parallel thereto.

In order to make the working clearer by an example, suppose that a subscriber whose line is served by the switchboard under consideration wishes to bring the point of his board into contact with the wire of another subscriber whose line is connected with that contact which is in the third line from the right of the switchboard and occupies the iifth place from the point in that line. The carriage F being'at the extreme right andv the carriage F2 at the front of the board, the subscriber will, by the means to be described below, send the' currents which shall advance the carriages F F2 three steps to the left and the carriage F2 four steps back. At this moment the point of his board will make the desired contact, and through it and the electrical connection which it has with the line of the desired subscriber the two subscribers will be put in communication with each other.

At the end of the travel of the carriage F is an electromagnetll, Fig. 1, and an electromagnet l2 is similarly arranged at the end of the travel of the carriage F2. The object of these magnets is to cause the quick return of the carriages to their respective startingpoints. To this end each of these return magnets is provided with an armature 13, which normally holds down the bar 14 against the pressure of a spring 15 that tends to raise it, the bar 14 being fastened to arms of the rock-shaft 14', which turns in its bearings when the bar 14 is raised or lowered. The spring 15 for the bar 14 of electromagnet E is clearly shown in Figs. 1 and 3. YSo long as the bars 14 are depressed below the level of the ratchet 7 by the armatures of the electro magnets 11 and 12, the pawls of the carriages engage the ratchet-teeth 5 but as soon as either of these electromagnets receives a current its armature is attracted and releases the correspondin g bar 14, which is thereupon raised by its spring 15 andV lifts the pawls out of engagement with their respective ratchet, so that the carriage being no longer held by its pawls can be drawn back to its startingpoint by a spring. A .very powerful spring is used for this purpose, that for returning the carriage F2 being marked 16 and that for the carriage F being marked 17. The spring 16 returns the carriage F2 when a current passes through the electromagnet 12, and the spring 17 returns the carriage F when the electromagnet 11 is energized by a current. The spring17 is placed near the end of a lever 18, fulcrumed at 19 on the frame ofthe ebonite plate and connected at 2O by a link with the carriage F. The vspring 17, being placed very near the fulcrum 19, is compressed or expanded through a very small distance for large movement of the carriage F. For a like reason the spring 16 for returning the carriage F2 is placed very near the fulcrum4 with the plate t4.

movement of the carriage F2. The point S is, of course, supported by the carriage F2, and to maintain the equilibrium of the whole system, so that the two carriages move always in a perfectly horizontal plane, a wheel 25, Fig. 4, and a slide 25 are arranged to run on thev side MN of the frame of the ebonite plate, and a wheel 26, Figs. 1 and 3, on the opposite parallel side of said frame.

Parallel with the ratchet of carriage F are arranged- First. A metallic plate t', insulated from all the other parts of the mechanism and presenting a series of metallic contacts, Figs. 1bis and 15, between which ebonite or other insulating material is interposed. The metallic parts have the same length as the ebonite parts, and a tooth of the ratchet corresponds to two parts of metallic plate t-that is to say, to a metallic and anv ebonite part. spring or brush t2, Figs. 1bis and 15, fastened in the carriage F', rubs (during the movements of the carriage F) lengthwise of the piece t', passing thus successively at each shift of the carriage over a non-metallic and a metallic part. When the carriage is at rest, the spring t2 bears upon an insulating part, and if the kcarriage F advances one tooth of the ratchet the spring t2 comes again over an insulating part of the piece t', after having crossed over the metallic part comprised between the two insulating parts just referred to. A second spring or brush t2 is fastened on the carriage F in electrical contact therewith. When said carriage is at the beginning of its course-that is to say, before it has been shifted-the metallic spring t2 is in contact with the the metallic plate t, Figs. 1bis and 15; but as soon as the carriage F is shifted, even the length of one tooth, the spring t2 leaves the plate t4.

Second. A second plate f6, like the plate t', has a succession of metallic parts with insulating parts of equal length between them, Figs. 1bis and 15. rlhe metallic and insulating parts of the plate f6 alternate with those of the plate that is to say, (contrary to what has been explained with reference to .F-the spring t2 (which is in electrical connection with the carriage F) bears on an insulating part of the platet, the spring t5 (which is insulated from the carriage F) bears on a metallic part of the plate f6, and, lastly, the spring 3 (which is in electrical connection with the carriage F) is in contact When the carriage F has advanced the length of a ratchet-tooth, the springs t2 and t5 occupy like positions, but the spring t2 is no longerin contact with the plate IOO ITO

t1. During this advance of the carriage F, the spring Z2 passes over a metallic part of the plate t and the spring t5 passes in like manner over an insulating part of the plate f6.

Referring now to the carriage F2, the following devices are arranged parallel with the ratchet corresponding with this carriage and lengthwise ot which said carriage moves, namely:

First. A platef, similar tothe plate f6 and commencing, like it, with a metallic part. Over this plate rubs a brush composed of one end ot the spring t, which is fastened to the carriage F2, withinsulating material interposed, and whose other end rubs over a metallic band f2, Figs. 1bis and 15. This band, however, commences with the second tooth of the ratchet, and at the start, when the carriage F2 has not moved, the brushes composing the spring ZG are in contact one with a metallic part of the plate f andthe other with a plate f2. Then the carriage F2 has been shifted the length of one tooth, one end ot the spring Z6 breaks contact with the plate f2 just above mentioned. l

Second. A plate t7, Figs. 1 aud 12', similar to the plate Z', and like it commencing with an insulating part; but the first metallic part corresponds with the second tooth of the ratchet. Commencing with the second movement of the carriage F2 a spring-brush Z2 moves lengthwise of this plate t2.

The object of these different plates will be explained below, when we Colne to consider the electrical connections.

Outside of the ebonite plate over which the carriages are shifted, and very near said plate, is a third electromaguet E2, Fig. 15, which on the passage through it of an electric current attracts the armature 27, Fig. 13. This armature is provided with an extension 28, Figs. 7 and 13, which carries a link 2f), at the extremity of which is a pawl 30 for acting upon the ratchet-wheel ll', Fig. 7, keyed on the vertical axle O2. On the attraction of the armature 27 the link 29 descends and forces the pawl 30 to turn the wheel ll in the direction of the hands of a watch. A stop-pawl 30' acts as a brake and regulates the rotation of the ratchet-wheel H', so that it turns one tooth at each attraction ofthe armature 27. On the axle O3 (which is put into motion by the ratchet-wheel ll) are fastened, first, a metallic wheel a", Figs. 7 and 72', insulated from the axle Oand provided with four projecting parts ZZ' Z2 Z2, placed at the ends of two diameters at right angles to each other. Second, an ebonite wheel H2, which carries four metallic strips forming two groups of two parallel strips each, the two groups being perpendicular to each other. The ends of these strips Zt h2, h2 h4, h2 h5, and h hl are curved downward, Fig. 7b, and are adapted to rub over a number of electrical contacts, as explained below. So also are the projections Z Z Z2 Z of the ring r', it being understood that the ends of the metallic strips of the wheel Il3 cannot touch the contacts over which the projections Z Z Z2 Z2 move, and, reciprocally, that these projections cannot touch the contacts over which move the ends of the metallic strips. Third, the ratchet-wheel Il', before mentioned. This wheel is fastened directly on the axle O2, without interposition of insulating material. Ithas twentyteeth. Fourth, in the last place, wholly above the ratchetwheel Il and out of contact with it, is a disk H2, whose circumference is divided into forty parts, of which twenty are metallic and twenty ot insulating material. Two brushes ll4 and H5, Fig. 7, rub on the circumference of this wheel. The object of all of these wheels will be explained below in considering the electrical communications.

At the side of eachebonite plate is the special electromagnet-relay R, Figs. 6, 6M, and 15, which is arranged as follows: lt is in the form of a horseshoe, and one ot its poles is divided into two branches Q2 Q2, on which are the bobbins q q2. Above the horseshoe is an ebonite plate q2, over which are fastened two metallic bars g4 (15, provided with adjustable co11taet-screwsQand q2. Between the branches Q2 and Q3 is a small armature q2, movable about a pivot Q and passing through a hole in the upper pole of said magnet R. The wires of bobbinsq q2 are so wound that when they are traversed by a current in a given direction one of them (say the bobbiu q) tends to strengthen the magnetism ot' the core Q2, while the other q2 tends to weaken the magnetism of the core Q2. 'It the current be in the opposite direction, the magnetism increases in the core Q2 and diminishes in the core Q2. It follows from this that in the first case the armature q2 is attracted toward the core Q3 and in the second case toward the core Q2. To prevent the armature sticking to the cores it is provided with small springs qo. It the subscriber whose line enters this electromagnetic relay sends positive or negative currents through the bobbins q and q2, the armature q2 is attracted toward one or the other of the cores and touches at its upper part the contactpiece q or (17, according to the direction of the current. The armature q2 being connected, as indicated in Fig. 15, with the positive pole of the central-office battery, the battery-current therefor will be directed, according to the position of the armature, either to the screw QG or the screw Q7. The object and operation of this relay will be considered below in explaining in detail the electrical connections of the central office.

The apparatus at the subscriber-s house may, in a telephonie point of View, be of any system. In the description it will be supposed that the telephone employed is of the Ader system, (generally adopted in Franeeg) but it should be observed that our invention has nothing to do with the telephonie apparatus proper, but only with certain accessory arrangements, and that these may be used in conjunction with no matter what telephonie lIO IZO

apparatus, as well as with that of the Ader system.

All the mechanism which we add to the telephonic apparatus is arranged above the telephones in a box, on the face of which are placed diverse buttons and indicators for the manipulation of our system. This mechanism is composed, essentially, of an electrom agnetic relay U, Fig. S, identical with the electromagnet R at the central oiice, of three ordinary electromagnets E4 E5 E, and of a commutator K. (Shown in detail in Figs. 1l and 11353.) This commutator consists, essentially', of a drum of insulating material, with two metallic bars K2 K3 of rectangular cross-section extending through it. These are insulated from each other and form at the surface of the cylinder four metallic contacts. Two other metallic contacts K4 and K5 are, moreover, fastened to this ebonite cylinder and are connected electricallyT with each other by a wire which goes through the commutatordruin. The two plates K4 and K5 extend, as shown in Fig. ll, around the drum, except for two spaces corresponding with the ends of the bars K2 and K3. About the cylinder of the com mutator are arranged the springs T T2 T3 T4 T5 T6 T7. These press against the cylinder, are insulated from one another, and are connected in circuit, as explained below. On one end of the commutator-shaft is fastened the toothed wheel P4, which meshes with the toothed Wheel P2, keyed on an auxiliary shaft, Fig. 8. The toothed wheel P3 is keyed on the same shaft and engages the toothed wheel P', which is subjected to the action of a spiral or other spring tending to turn the wheel P', and consequently the commutator K. The spiralspringis rewound when necessary by means of a crank P, Fig. l2, on the front face of the box which holds the mechanism.

As shown in Fig. ll, commutator K is so mounted as to be movable in the direction of its axis. Normally it is constantly pressed against the front face of the box by the action of the spring 34, and it is prevented from turning by the pin v4, which is inserted into one of the holes 'U5 in one of the faces of the commutator, Fig. S. So long as the operator fails to press the button V the pin U4 remains in its hole 'U5 and holds the commutator from turning; but on the operator pressing in the button V the lever v3 is turned on its fulcrum, the pin Q24 is Withdrawn from the hole o5, and the commutator begins to turn under the action of the spiral spring. It' instead of pressing in the button V the operator presses upon the button V2, he will turn the lever o5 on its fulcrum, as shown in Figs. 1l and 11555, and this will act upon the lever v7, which will shift the commutator in the direction of its axis, at the same time compressing the spring 34. By this lateral shifting of the commutator the pin o4 is freed from the hole v5 in which it has been, so that the commutator is again free and can turn under the action of the spiral spring. In this latter case, the commutator being shifted lengthwise of its axis, the position of the bars K2 K3 and plates K4 K5 will be altered selectively to the contact-springs T T2 T3, 85e. The purpose of this will be explained below. Three other buttons V3 V4 V5 are arranged on the apparatus, the button V3 connected with the end of leverfn, which carries three fingers or metallic contacts *c2913 n3. Normally--that is to say, when no pressure is exerted on the button V3-the lever/n is maintained by spring nl in the position shown in Fig. 9; but if the operator presses upon the button V3 the lever 'n' will turn on its fulcrum and will bring the nger n3 in contact with the plate n3 and will cause the ngers n3 'n2 to make contact, successively, with. the plates n4 m5 n3. On removing the pressure on the button V3 the spring a7 will bring the lever 'n' back to its primitiveposition. 'lhebuttonV4isconnected with the end of a le'verm3, Figs. 8 and l0, which has three fingers or contacts m,m2, and m3 at its other end. By exerting a pressure on the button V4 the finger m2 is brought into contact with the plate m5. By continuing'the pressure the finger m is brought into contact with the plate m3, finger m2 into contact with plate m4, and finger 'm3 into contact with plate m5. On removal of the pressure the lower lever m3 will return to its primitive position under the influence of the spring m7, and during such return the finger m will abandon the plate m3, while the fingers m2 m3 will pass again over the plates m4 and m5.

It has been said above that the essential organs of the mechanism of the subscribers house apparatus were an electromagnetic relay U, identical in construction with the electromagnet R, and three ordinary electromagnets E4 E5 E5. The electromagnet U, like that before described, has for its object to distribute the currents. The electromagnet E4 controls an armature e4, to which is jointed a link p', connected at its upper end with a bar p3, that carries a pawl p2 and is pivoted on the shaft W. A spring constantly holds the pawl against the teeth of the ratchetwheel W2. On sending a current into the electromagnet E4 the armature e4 is attracted and the link p and pawl p3 are drawn down, the pawl riding idly over a tooth of the ratchet-wheel. As soon as the attraction of the electromagnet E4 ceases, through the interruption of the current, the spring TV5 returns the armature e4 and pawl p2 and turns the wheel W2 one tooth. The shaft'W of the ratchet-Wheel W2 has mounted thereon a circular lplate W3, provided vnear its circumfer ence with a pin W6. When the wheel W3 makes a com plete revolution, the tenon, meeting the teeth of the wheel W4 at its side, will turn this latter one tooth. It will be readily understood, without its being necessary to dwell overlong upon it, that if the shafts of wheels W4 W2 carry disks on which are inscribed the figures l, 2, 3, 4,

IOO

IIO

H 5777 (l 6,73 7,55 l 8,7, (C 9,?) C 0,37 can indicate the number of currents which traverse the electromagnet E4, one of them exhibiting units and the other tens, provided the ratchet-wheel W2 has ten teeth, and also the wheel W4. rlhe counting-wheels VZ Wl can evidently be supplemented by a third wheel for hundreds, and so on. They coustitute, in fact, the mechanism of the ordinary register for indicating the number of rotations. In the front face of the box which holds the sub-station apparatus are two openings CZ and (Z2, through which the operator can observe the numbers ot the just-mentioned disks as they pass in succession.

The electromagnet controls a system of toothed wheels identical in construction with that just described, so that the operator can, in like manner, by observation of the number appearing at the openings CZ3 d4, note the number of currents which have passed through the coils of electromagnet E5. It is well to mention, however, a peouliarity in the system of toothed wheels belonging to the elcctromagnet E5. When the two disks are at zero-that is to say, when no current has traversed the electromagnet liG-a pin i3, fixed on the wheel t2, holds the bent lever t4 in the position shown, notwithstanding the pressure of spring t5; but so soon as the wheel i2 has been turned one division by the excitation of the electromagnet E5 said lever 4, being no longer held by the pin t3, turns on its fulcrum t" under the force of spring i5, Fig. S. The upper arm of the bent lever rests upon the contact i@ in the position shown; but it leaves the contact ZG and moves over to the contact il when the lever t* is released by the pin i3. The object of this change of electrical connection will be explained below.

The electromaguet EGis arranged to attract an armature Z7, and thus, through the link Z8, to turn the lever Z, which is pivoted on the shaft l7'4 and carries the pawl Z4. This last is s0 arranged that when the armature Z7 is attracted it rides idly over the teeth of ratchet-wheel Z5. A spring Z6 brings the armature Z7 back to its iirst position on the cessation of the current in the coils of the electromagnet E, and in so doing it causes the pawl Z4 to turn the ratchet-wheel Z5 one tooth. This ratchetwheel is mounted on the shaft j4, which carries, moreover, a gear-wheel for engaging the wheelf. 0n the same shaft as the WheeljG a wheel j is mounted, which is provided with four projections at the ends, respectively, ot two diameters which cross each other at right angles. Two of these projections (at opposite ends ofthe same diameter) are in contact with the metallic platesjf, Fig. 8, when the apparatus is not in operation. The wheel 7" carries on its front face a disk divided into four sectors, which have, respectively, the inscriptions Rest, Calh Ring, Talk, or the like. The operator can see the inscriptions one at a time through the window d5. At the start, before any current has passed through the electromagnet E, the word Rest is Visible through the window (Z5.

The button V5 at the side of the apparatus is for bringing the wheels back to zero, which are controlled by the electromagnets E'l El. lt is not important to use this button in connection with the numbering-wheels, but any appropriate arrangement can be employed.

Having thus described the different organs which go to make our new system of automatic switching apparatus for telephones, theiroperation will next be described, together with the electrical connect ions ofthe different organs. To facilitate this explanation there is represented diagrammatically on Figs. l5, l5, and 15b, first, a central oftice with three subscribers switchboards; second, the three sub-station apparatuses at the subscribers houses. It should be observed, however, that the central oftice, such as herein described [or three sub-stations, can, without other ineditication, receive two hundred and twenty-two additional switchboards, each of the switchboards represented in this figure having two hundred and twenty-tive available contacts and each subscriber being thereby able to put himself in connection, at his fancy, with any one of two hundred and twenty-four subscribers, and it being understood that what is said about the lower plates C D applies to the upper plates.

The central-office battery is divided into two parts, as shown in Figs. l5, 15, and 15". The wire 40 corresponds with the positive pole of the battery, the wire #ll with the negative pole, and the wire 42 being grounded.

Taking the switchboard X and the corresponding sub-station, the electrical connections will be explained with reference to them, and these connections, it will be understood, are similarly established on the switchboards Y and Z and the sub-station apparatus corresponding thereto, respectively.

The line-wire 43 enters the central ottico and terminates in the metallic band 44, extending below all the switehboardsot the oftiee and having a terminal contact in every one of them at a position assigned in them to the subscriber X. In the example chosen all the contacts whose abscissas are 4 and the ordinates 3 are connected with the band 44;, constituting a prolongation of the line-wire ot the subscriber X. The band 45, which corresponds with the line-wire of subscriber Y, is in like manner in communication with all the contacts which in the several switchboards have 2 for their abscissas andi for their ordinates. Similarly the band 45, which corresponds with the line-wire of subscriber Z, is connected with all the contacts which in the several switchboards of the office have 3 for their abscissas and 5 fortheir ordinates. The line-wire t3 of subscriber X is also connected with the coils of the relay R, and through such coils and the wires 46 and 4t2 is led to ground. Suppose the subscriber X wishes to put himself in communication with the subscriber Z,

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llO

IZO

the contacts of whose line-wire are represented by the fraction Lg-that is to say, 3 for the abscissas and 5 for the ordinates, for it should be understood that the subscriber of an exchange on the present system, in place of being designated by a number, would be designated by a fraction whose numerator would represent the abscissas and the denominator the ordinates of the appropriate contact on the switehhoards. The subscriber X should then, to bring the movable point S of his switchboard over the contact correspending with the line of subscriber Z, cause said point to move three steps in the direction of abscissas and six steps in that of ordinates, for the point S', when at rest, touches the plate S4, which has a length of two contacts in-the direction of ordinates, so that to arrive at the rst line of abscissas the point S must travel two steps in the direction of ordinates. By pressing on the button V at his sub-station the subscriber X frees the commutator K of the sub-station apparatus, (as before explained,) and this turns so long as the subscriber X continues to press in the button V. As the commutator is put into motion the ends of the bar K2 are brought into contact with the springs T and T5, while the ends of bar K2 come into contact with the springs T2 and T6. The spring T is connected by the wire 47 with the negative pole of the sub-station battery and the spring T5 is grounded by the wire 48. Hence the contact of the ends of bar K3 with the springs T2 and TG serves to ground the negative pole of the sub-station battery. The spring T2 is connectedhy the wire 49 and 60 with the positive pole of the battery and the spring T5 is connected by the wire 50 with the line-wire 43. Hence the contact of the ends of the bar K5 with the springs T2 T 5 puts the positive pole of the battery to line. A positive current therefore travels over the line 43 and passes through the coils of relay R and wires 46 and 42 to the ground, which conducts it to the wire 4S, and it then goes by the spring T, bar K2, spring T5, and wire 47 to the negative pole of the battery. Under the inuence of this current the armature g8 of the relay is attracted by the core Q2 and the upper end of said armature touches the screw g5. The armature q2 is permanently connected by the wire 5l with the positive pole of the central-office battery and the screw Q6 is connected by the wire 52 with the plate f. A current therefore travels by way of the wire 5l, armature q2, screw g5, and wire 52 to the plate f. From the plate, Fig. 121s, the brush t5, in contact with a metallic part of said plate, delivers the current to the plate f2, (inasmuch as the carriage F2 has not yet moved.) Thence the current passes by the wire 53 to the electromagnet E', and at'ter passing through its coils it returns by the wires 54 and 4l to the negative pole of the battery. The electromagnet E is thus energized and attracts the armature andvpawl ready to shift the carriage F a tooth of the ratchet 7, Fig. l, so soon as the current shall be interrupted.

In Fig. 15 the organs of the switchboard of subscriber X are shown in the position occupied after the carriage F has been advanced three steps and the carriage F2 six steps, while the organs of the switchboards of subscribers Y and Z are in their initial positions.

As the positive current sent to line by the commntator K ceases (that is to say, as soon as the ends of the bar K2 are no longer in contact with the springs T2 and T6) the armature q2, being no longer attractedby the core Q2, resumes its rst position between the two cores and the circuit of the armature E is broken and the carriage F is advanced one step. This circuit will not be closed again until after a selnirotation of the commutator, when contact is made again between the ends of the bar K3 and the springs T2 'Ii and a positive current sent, as before, through the relay R. Reverting now to the central ofce at the moment when the first positive current from the subscribers station stopsthat is to say, when the ends of the bar K3 have left the springs T2 rIG-the circuit of the electromagnet E is interrupted and the carriage Fadvances a tooth on the ratchet 7, as has been already stated; but during this advance the brush t2 on the carriage F has rubbed over a metallic part of the plate t', and consequently has put the carriage F in electrical connection, by the wire 55, with the negative pole of the centraloffice battery. The carriage Fl is connected by the wire 5G with the line 43, and consequently on the passage of the brush t2 over a metallicpart of the plate t the line 43 is put into connection with the negative pole ot' the central-office battery. A negative current therefore enters the relay U by the wire 57, passes through its coils, goes by the wire 5S to the spring T4, passes between plates K4 and K5 of the commutator, and goes by spring T7 and wire 4S to the ground, which returns it to the battery at the central ofce. It will be observed that the plates K4 and K5 only allow the circuit of the relay U to be closed when the bars K3 K2 of the commutator are not in position to send a'current to line, or, in other words, when there is no current on the line, since the intervals between the plates K4 and K5 correspond,on the circumference of the commutator, with the ends of the bars K2 and K5. The before-mentioned negative current causes the relay U to attract its armature M5 toward the core U3 and to bring its upper end against the screw ue, and, inasmuch as the said armature is connected by the wire with the positive pole of the sub-station battery, a currentis thereby sent over wire 60, screw 11,5, and Wire 61 to lever t4, thence by contact t5 and wire 62 to the electromagnet E4, thence, after traversing its coils, by the wire 47 to the negative pole of said battery. This electromagnet is thereby energized and attracts its armature e, which on its release advances the wheel W2, as be- IOO IIO

fore described, and thereby causes the gure l to appear at the window d2. It should bc observed that the negative current from the wire 5G divides, a part only passing through the relay U, the other part passing the relay R at the central office. The armature qS is then attracted toward the cere Q2 and touches with its upper end the screw (j, which is connected by the wire G4 with the electrolnagnet E2. This last is in its turn connected bythe wire G5 with the contact r2, Figs. l5, 7, and 7b, which at this moment is in elcctricalconnection, by the projections Z Z3 of the wheel fr', with the contact r3, that is connected by the wire G6 with the plate f, Fig. 1mi". To this point, therefore, the circuit of the electroinagnet E2 is closed from the central-office battery by wires 40 and 5l, armature QS, screw ql, wire G4, electromagnet E2, wire G5, contact r2, wheel i", contact r3, wire GG, and platef; but at the moment when a current might otherwise pass-that is, when the negative current is sent from the central office to the subscribers station-the spring t5, which is connected by the wire (57 with the negative pole of the central-office battery, is in contact solely with an insulating part of the platefso that at this moment the circuit of the electroniagnet E2is open at the plate f6, and it hence follows that the negative current sent from the central office to the sub-station by the centraloffice battery has no effect on any organ at the central office, except to produce an idle movement of the relay R.

After the action of the negative current on the electromagnet E4 has taken place a new positive current is sent fro-m the substation to the central oflice through the continued rotation of the commutator-drum K', and this is followed by a negative current from the cen tral office to the sub-station, and this succession of a positive followed by a negative current is continued so long as the subscriber pushes in the button V. In the case supposed the subscriber would release the button as soonas the ligure 3 should appear at the window d2, since the abscissa of the subscriber Z, with whom the subscriber X is supposed to wishto communicate, isequal to three.

After releasing the button V the subscriber will press in the button V2. The pressure exerted on this button V2 has the effect (indicated in Fig. llbis and hereinbefore referred to) of moving the commutator, so that the ends of the bar K2 will (through the rotation of the commutator-dru 1n K) make contact with the springs T2and T2, while the ends of the bar K3 will make contact with the springs T3 and Tf. Pressure on the button V2 also has the effect of freeing the commutatordrum (as before described) and allowing it to rotate.

The rotation of the commutator, when pressed back by means of button V2, first brings the ends of the bar K2 in contact with the springs T2 T5 (which will have no effect on the tine, but simply ground the positive pole of the battery) and the ends of the bar Kin contact with the springs T2andr`. As the spring T3 is connected by the wires (3S and 47 with the negative pole of the sub-station battery and the spring T with thc line, a negative current will be sent from the substation battery over the line to the relay It at the central oflice and will return by the ground and the springs T2 Such current causes the relay lt to attract the armature q2 toward the core Q2 and to bring the upper end of said armature against the screw (17. The making of this contact completes the circuit of the electromagnet E2, which circuit includes the wire 64, (from the screw (17,) the electromagnet E2 itself, the wire G5, contact r2, the projections l and t3 of wheel fr', the contact fr3, the wire GG, the platef, the spring t5, and the wire 67. This circuit is now complete when the armature g8 touches the screw (17, because the spring t5 is in contact with a metallic part of the plate f6. The electrolnagnet E2is thus traversed by a current which retracts the armature of said magnet for feeding the earriage E2 a tooth of its ratchet, as before explained. vWhen, through the rotation of the commutator, the ends of the bar K3 leave the springs T3 and TG, the negative current stops, the armature g2 resumes its position, and the circuit of the electromagnet E2 is opened. The commutator K continuing to turn a second negative current is sent from the subscribers station tothe central office and the carriage F2 advances a second tooth; but at this instant areturn current, like that sent when the button V was pushed in, although by another part of the apparatus and of the contrary polarity, (being positive new instead of negative, as before,) is sent automatically from the central ofiice to the sub-station in the following manner: The plate t7, over which the spring t2 on the carriage F2 slides, is connected by the wire (59 with the positive pole of the central-office battery, while the carriage F2 is connected by the wire 70 with the line-wire 43. Therefore at the moment when the spring t8 on the carriage F2 passes over a metallic part of the plate t2 a positive current from the central-oflicc battery passes over the wire 69, plate t7, spring t, carriage F2, wire 70, and line 43 to the relay U at the subscriber-s station. This current passes through the coils of the relay U, and goes thence by wire 58, spring T4, metallic pieces K4 K5, spring T7, and wire 48 to the ground, which conducts it back to the central ollice. This positive current passing through the relay U causes it to attract its armature ft/j" toward the core UA1 and to bring its upper end against the screw u?, whereupon, as has been before shown, the circuit of the electromagnet E5 will be closed, the armature 11,5 being connected (as said before) by the wire 60 with the positive pole of the sub-station battery. The current passes by wire (30, arma! ture a5, screw a7, wire 7l, plate y2, wheel j', plate 32, wire 72, electromagnet E5, and,

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finally, the wire 47, which terminates at the negative pole. The current in traversing the electromagnet E5 attracts its armature ready forits release to cause the figure l to appear at the window d4. So long as the operators finger holds in the button V2 the same phenomena are repeated in the same order-that is to say, a negative current will go from the sub-station and a positive current (which is a sort of controlling-current) will come back from the central office for indicating to the subscriber the number of steps taken by the carriage F2. For reasons like those given above the positive current sent from the central ofce to the sub-station produces no effect on the organs at the central office beyond the contact of the armature g8 with the screw Q6, for (the carriage F2 being moved) the spring t6 is no longer in contact with the plate f2, (which is connected with the eleetromaguet E,) but with the plate f3, and, moreover, at the moment of sending the positive current the other end of the spring t6 is moving overan insulating part of the plate f. The circuit of the electromagnet E is therefore interrupted at both points and no current can pass through it. The subscriber continues to press with his finger on the button V2 until he sees through the Windows d3 al4a number equal to the denominator of the fraction of the subscriber with whom he wishes to be put in communication. In the case supposed of his Wishing to be put in communication with the subscriber Z he would retain his finger on the button until the figure 5 appeared at the window d4. At this instant the point S of Xs switchboard will be on the fifth line of abscissas, although the carriage F2 has advanced six steps, for it should be observed that the first step of the carriage F2 sent no controlled current to the sub-station, the point t8 being out of contact with a metallic part of the plate t7 during such first step. These primary operations having been effected, the point S will be on that contact of the subscriber Xs switchboard which is connected with the line-Wire of the subscriber Z. When the subscriber X has placed his point S on the proper contact, the present function of the electromagnets ceases, since they have no other purpose than to move the carriages F" F2. Their circuits should therefore be broken, or, in other words, these electromagnets should be blocked. So far as the electromagnet E is concerned this has been already effected, for from the time when the carriage F2 has passed over the first tooth of its ratchetthat is to say, after it has abandoned its initial position-the spring t6 has left the plate f2, which is connected with `the coils of the electromagnet E and has been transferred to the plate f3, which is connected with the coils of the magnet E3. The spring t6 rests in contact with this plate f2 unto the end of the travel of the carriage F2. It follows from this that positive currents acting on the electric relay R would no longer cause the eXcitation of the electromagnet E', but of the electromagnet E2, provided such positive currents were sent at a time when the spring t6 touched a metallic part of the plate f In an analogous Way the circuit of the electromagnet E4, which is at the subscribers station and which corresponds with the electromagnet E at the central office, has had its connection with the screw 'a6 interrupted, for as soon as the Wheel i2 has turned a tooth the lever i4, being no longer held by the pin 3, is turned by the spring t5 and made to rest upon the contact 717, so that thescrew a6, in place of connecting with the electromagnet E4, connects by the wire 61, lever i4, contact 7, and wire 8O with the finger fris, fastened to the end of the lever n', which is controlled by the button V3. As'eX- plained below, this finger 'a8 closes at the proper time the circuit of the electromagnet E6. The electromagnet E3 at the central office serves in its turn to break the circuit of the electromagnet E2, the action being as follows: After the subscriber X has ceased to press in the button V2 he presses in the button V3 in order to send to the central ofce, first, a positive current; second, a negati-ve current, and, third, a positive current again. When the lever 'n' turns on its fulcrum in the direction of the arrow, Fig. l5, the fingers 'n2 n2 slide over three metallic contacts n4 fc5 'n'. The contact a5 is connected with the negative pole of the sub-station battery by the wires 8l and 47 and the contacts n4 and n@ with the positive pole by the wires 82 and 83. The lever fn', when turned by the pressure on the button V2, brings the finger n2 over the contact n4 and the linger n3 over the contact n. Since the finger n2 is connected by the wires 84 and 50 with the line and the finger n3 by the wires 85 and 48 with the ground, when they touch the contacts 'n4 ns, respectively, a positive current is sent over Wire 82, contact n4, finger n2, Wires 84 and 50, line 43, relay R, Wire 46 to ground, from ground to wires 48 and 85, finger n3, contact a5, and Wires 8l and 47. The fingers n3 n2 are of course insulated from the lever n.

The positive current energizes the relay.

electromagnet R and causes the armature to make contact with the screw q, thereby closing the circuit of the electromagnet E3. This circuit ineludes the wire 5l, the armature g8, the screw q", the wire 52, the platef, the spring t6, the plate f3, the Wire 86, the electromagnet E3, the wire 87, and,lastly, the Wire 4l, which terminates in the negative pole of the battery. The positive current in passing through the electromagnet E3 produces the attraction of its armature 27, Fig. 13, moving it and the armature-lever 28, Figs. 7 and 13, and forcing down the link 29 and pawl 30, so as to turn the ratchet-wheel H one tooth.

The ratchet-wheel in turning carries with it the shaft O3, (on which it is fixed,) and consequently the wheel r will be moved also an amount which corresponds with a' tooth of the IOO IZO

the contacts r2 0'5 and make connection with` contacts T495. The action of the positive current sent through the electromagnet E5 is therefore to open the circuit of the electromagnet E2, which is thus blocked and further movements of the carriage F2 prevented. In addition to this the positive current causes the movement of the wheel yr' and brings the projections Z Z2 over or into connection with the contacts r4 9'5. The contactr5 is connected by the wire 00 with the line-wire andthe contact r1 with the point S by the Wire 9i. Besides the connection between the point S and the contact o this point S is connected bythe wire 02 with a plate t1, which makes contact with the point Z2, Figs. l and l5, fast on the carriage F, that is itself connected to line by line-wire 56, so that when the carriage F is in its original position, Fig. l5, the point S is in electrical connection with the line by the wire 92, the plate t4, the point Z5, the carriage F', and the wire 5G; but as soon as the carriage F is shifted, as a result of the action of the subscribers finger' on the button V', the point t3 leaves the plate Z", andthe point S is thus, after the first step of carriage F', without a line connection until such a connection is re-established by the electromagnet E5, as just described. This` temporary interruption is made between the point S and the line in order to eliminate the influence of the currents which serve to shift the point over the contacts of the ebonite plate, for otherwise these currents, entering the contact-line of some other subscriber, would pass to the point of this subscriber, and from there into the aerial conducting-wire, thus putting in motion apparatus foreign to the communication desired.

The movements of the distributing-wheel r are governed automatically from the subscribers station. The shaft O5 has keyed thereon, as before explained, a wheel H2, Whose circumference is provided with alternate metallic and insulating parts. Two brushes Htand H5 bear on this wheel. One of these brushes H5 is connected bythe wire lOO With the line-wire 43, whereas the other brush H4 is connected by the wire 97 with the negative pole of the central-office battery. Before the Wheel r has moved-*that is tosay, while the projections Z and Z3 are over, respectively, the con- Iacts q2 and v5the brushes ll4 and H5 bear on portions of insulating material, and consequently nothing happens. lVhen the wheel o" turns one tooth, the wheel i12 turns equally, and the brushes Il4 and H5 rub during this movement over metallic portions to come to rest upon portions of insulating material. A circuit is thus established during said movement, which circuit includes the battery, the wire 97, the brush H4, the wheel H2, the brush ll5, the wire 100, the line-wire 13,the wire 57, the electromagnet U, the wire 58, the spring T4, the plates KL K5, the spring T7, and wire etS to ground. The circuit of the electromagnet U is therefore closed when the brushes Il4 and H5 bear upon the metallic parts of the wheel H2, and the electromagnet U is traversed at this moment by a negative current coming from the central office. The armature a5 then comes into contact with the screw u, which closes the circuit of the electromagnet E5, this circuit being composed ofthe wire GO, (leading from the positive pole of the sub-station battery,) the armature a5, thc screw u, the level' t, the contact z5, the Wire SO, the finger as, the plate n, the wire 10i, the electromagnet E5, and the wire 102, which leads to the negative pole of said battery. The ci rcnit of the electromagnet E5 being thus closed it attracts its armature, and when the current stops the ratchet-wheel Z5 is turned by the spring Z6 and pawl Z4. The wheelj5 is mounted on the same shaft as the ratchet-wheel Z5, and a wheel j', divided into four sectors, is controlled by a toothed wheel keyed on the shaft of wheeljfi, so that when the ratchet-wheel has turned a tooth the wheelj is shifted aquarterof aturn. The wheel j is divided into four sectors, on which are the following inscriptions, respectivelynamely, Rest, Call, Ri1ig,ax1d `alk. At each turn of the wheeljl these inscriptions (commencing with Rest) appear, one after the other, at the opening The object of these inscriptions is as follows: XVhen the sub-station apparatus is in the state of rest, the inscription Rest is shown through the opening (Z5, and so remains exposed while the subscriber is manipulating the buttons V V2. lVhen he presses on the button V2, as we have seen, the first negative currentsent from the central office to the substation closes the circuit of the electromagnet E5, thereby turning the ratchet-wheel Z5 one tooth and the wheel j a quarter-turn and bringing the inscription Call into View through the opening (Z5. After having thus examined the effects of the positive current sent to the central office by the contact of finger n2 and plate n4 and ot' the controller-cu r- ICO rent sent from the central office to the substation consideration will next be given to the effect produced by the further movemeni, of the lever n under the pressure applied to the button V3. The fingers a5 and n4 are thereby brought into contact with the plates a5 and a5, respectively. A negative current passes by the plate a5, finger n2, and wires Si and 50 yto line, the contact of the finger a5 with the plate a6 serving to ground the positive pole of the subscribers battery. The negative current passes to ground through the relay R at the central office. The attraction of the relay R now brings the armature qs against the screw Q7; but inasmuch as the circuit of the electromagnet E2 is open the action of the negative current in the relay R is without effect upon the subscriber Xs devices at the central office. This negative current., however, goes by the wire 90, plate o5, projections Z5 Z, plate rt, and wire 91 to point s', and from this it passes over the contact-Wire 45 of subscriber Z to his contact SZ4 and point St. Frein the point SZ' there is a path for the current through the plate ZZ4, spring ZZ3, carriage FZ', wire 56Z, line-wire 432 and relay RZ to ground. The effect on the relay R3 is to bring the armature @Z3 against screw q", which thus closes the circuit of the electromagnet EZ3, so that this, being energized, draws in its armature for shifting the carriage FZ2 one tooth in order to block the electromagnet EZ by opening its circuit at the spring tZ3 and to connect the coils of electromagnet EZ3, by way of the plate fZ3 and spring t, with the screw QZ of the relay. From all this it follows that the negative current sent by the subscriber X produces the before-recited effects on the subscriber Zs switchboard, the point SZ being shifted one contact in thedirection of ordinates, without being brought, however, onto any of the subscribers contacts, for the plate SZ4.occupies two spaces in the direction of ordinates and is not connected with the subscribers lines.

The negative current sent by the subscriber X to the switchboard of subscriber Z not only produces the effects just examined,but it also passes over the line to sub-station Z and through the relay UZ to ground, this relay being operated to close the circuit of electromagnet EZiand cause the figure 1 Z to appear at the window d3. The first step of the carriage FZ2 produces no controller-current, as before seen.

To proceed now to the effect of the thirdl current sent by the subscriber tothe central office when the lever n' is returned to the initial position bythe spring a7, Fig. 9, on release of the button V3, this current, as has been said, is positive, forit is produced by a new contact between the plate n4 and the finger n2. It passes through the electromagnetrelay R and closes the circuit of the electromagnet E3, which acts again on the lever 28 and wheel r', turning said wheel through an are equal to a tooths length. Besides this first effect (which will be further considered below) the positive current also passes through the plate r3, the projection Z3, the wheel fr', the projection Z', the plate r4, the wire 91, the point S', the switchboard of subscriber Z, and the relay RZ, thus closing the circuit of the eleetromagnet EZ3. This elect-romagnet turns the distributing-wheel rZ' one tooth, (the first from the initial position.) In this manner (precisely as the corresponding change was before made in the apparatus of subscriber X) the circuit of the electromagnet EZ2 is opened and the connection through the wheel rz' of the point SZ with the line-wire to the sub-station Z is established. This positive current also goes to the sub-station Z and then closes the circuit of the electroniagnet E3, so that the gure 1 appears at the opening (Z4 and the circuit of the electromagnet EZ4 is opened. The wheel rZ' in turning sends, as is evident from what has been said, a negative current over the line-wire of subscriber Z, (that is, the controller-current.) This current passes through the electromagnet UZ and armature w3 is attracted and brought into contact with the screw a3; but this has no action on the organs of sub-station Z, since this attraction can only close one ofthe breaks in the circuit of the electromagnet EZ, this circuit being also broken between the finger nZ3 and the plato nZ9 when there is no pressure on the button V3. The two negative controller-currents, one sent by the wheel r' and the other by the wheell rZ',unite at the substation X, and passing through the relay U they close the circuit of the electromagnet E3, which closure is possible because the finger n3 is in contact with the plate n. The wheelj' is thus turned through a quadrant and the inscription Ring made to appear at the opening d3. Then the subscriber X, by turning the button M', Fig. 12, of his apparatus, connected to wheelj', causes the inscription Talk to appear, such movement of the wheel j' simply causing the rotation of wheel ,73 and ratchet-wheel Z3 a distance of one tooth under the pawl Z4. By such operation the disk j' is brought into proper position for the next succeeding movement to the F Rest position, which is effected by the magnet E3, as hereinafter explained. Thus, after the button V3 has been operated, the central-office apparatus belonging to the subscribers X and Z are in the following conditions: In the subscriber Xs apparatus, the movements of the point S' are blocked, and consequently the pointsS' SZ', in the two apparatus cannot be shifted farther. The distributing-Wheel r has advanced two steps from the initial position and the distributing-wheel rZ' a single tooth. The points s and SZ' are in connection with the aerial conducting-wires of the subscribers X and Z.

Negative currents sent by either of the two subscribers will have no effect on their respective apparatus, but every positive current sent by either will advance the distributingwheels r' and rZ' of both apparatus simultaneously one tooth.

The subscriber X, profiting by the fact that a negative current produces no effect in either apparatus, sends a call-signal by means of a bell. To this end, he presses on the special button of the Ader apparatus provided for ringing up, which (as the diagram indicates) sends a negative current to line. The subscriber Z', after having heard the call-bell, manipulates the button V3 of his apparatus,4 which (as explained above) produces three currents in succession-namely: a positive current, a negative current, a positive current. The tirst positive current closes the circuit of electromagnet EZ3, (which has the effect of turningthe distributing-wheel r' one tooth and also closes the circuit of the electromagnet E3, (which has the effect of similarly turning the distributing-wheel r',) so that after this positive current the distributingwheel r has been shifted three times and the distributing-wheel rZ' twice only.

The wheel rt in turning sends, as we know,

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a negative controller-ernment, which passes through the electromagnetic relay UZ and closes the circuit of the elect1omagnetEG,(in asmuch as the finger n touches the plate mm2) thus causing the word Call to appear at the subscriber Zs, but which has no action at the subscribcrXs (because, as already explained, the finger yn3 is no more in contact with the plate nn). Moreover, the wheel r in turning sends a negative controller-current, which has no effect on the apparatus of subscriber X, nor upon the switchboard of the subscriber Z, but which, passing through the sub-station Z, excites the relay U"A to draw over the armature ut and close the circuit of the electromagnet Ef, which has the effect of making the word Ring appear at the opening d". The wheel R', in turning the third time, produces certain additional eects, which will now be explained. Vhen the wheel r turns the third time the strip h2 h4 touches the plate r with one of its ends and the plate ru with the other. The plate r6 is connected by the wire 9i with the solenoid S2 of the point S', and the plate rl is connected by the wire 95 with the other terminal of the same solenoid. The plate 0" is connected by the wire 96 with the positive pole of the central-office battery, and the plate r with its negative pole. Vhen, therefore, the wheel r has turned for the third time, the strips h2 h4 and h3 h close the circuit of the solenoid. The winding of this s0- lenoid is such that when it is traversed by this current the point S (which is simply a perinanent magnet) is withdrawn from the lower plate C D (which we term the communication-plate) to the upper plate A B (which we term the conversation-plate) and the said point S (which, up to the present, has been in contact on thc plate C D with the contact corresponding with the wire of subscriber Z) presses against the contact of the upper plate, which likewise corresponds with the line of subscriber Z. In passing, it may be noted that it is not the subscriber X who has put himsefl into position to speak to the subscriber Z; but that only after this latter has pressed upon the button V3 of his apparatus is the point S' transferred to the conversation-plate. This has its importance, for, assuming for a moment that the two subscribers X and Z are conversing and that a third subscriber Y should wish to cut into their conversation, he would not be able to do so, since that would require the assistance of the two subscribers X or Z to bring point SY to the conversationplate. Thus, after the first positive current sent to the subscriber Z, the point S is against the contact of the upper plate AB and at the sub-station of Z, the wheel rz has turned twice, and the word Ring appears at the opening (F5.

The second (or negative) current, which the subscriber Z sends by pressing the button Vif, produces no effect either in this subscribers apparatus or in that of the subscriber X.

The third current, (a positive current,) sent by the same subscriber by manipulating the button V23, will act solelyon the relay R", because the subscriber X, whose point S is now in the contact-line of the platform A B, has no communication with the subscriber Z, whose point SY" rests on the contact-line of the platform C D. The action of this positive current on the relay R7A is to cause the wheel rz to turn for the third time,which movement effects (as explained above for the wheel r) the closure of the circuit of the solenoid S72, and consequently the transfer of the point S7" from the plate C D to the plate A B. It follows from this that after the manipulation of the buttonVZJ the subscribers X and Z are in commu'nieatiomand that, too, in such manner that no third party can insert himself,because the two points S and S7" are against contact of the plate A B and there remain until the signal, if given, which announces the end of the conversation-that is to say, as we shall see latex-,untilone of the two subscribers has pressed the button V1. The wheel r, in turning the third time, sends a negative controller-current, which acts in the sub-station Z to close the circuit of the electromagnet EZ and thereby to turn the wheel fr" through another quadrant and cause the inscription Talk to appear at the window It has been explained how the inscriptions Call and Ring present themselves in succession before the eyes ot' the subscriber X when he manipulates the button V3, but it is well to observe that (owing tothe rapidity of sending the currents bypressing the button V3) the word Call does not remain exposed, but gives place immediately to the inscription Ring On the contrary, at the station of the subscriber Z who is called, the negative currents which enter his apparatus are so produced when he manipulates the button V as that the inscriptions Call and Ring7 pass very rapidly, and the sole inscription Talk will remain exposed at the opening dt". It follows from this that the subscribers between whom the communication has been established cannot converse until the inscription Talk shall have appeared at the opening d'5 at the sub-station Z.

XVhen the conversation is ended, the subscriberX (who has put himself in communication with the subscriber Z) presses the button V4 and what the subscriber Z must do will be hereinafter explained. The pressing in of the button V4 has the effect of sending two positive currents in succession. The first is produced by the passage of the finger m2 across the contact m and of the linger prl across the contact m5. Then when the pressure on the button is relieved the fingers move back across the contacts m4 and mi', respectively, and a second positive current is sent. In the diagram, Fig. 15, the arrow7 shows the motion of the lever m8 when the button is pressed in.

Before considering the effect produced in the apparatus by the pressure exerted on the TOO IIO 

